National Hockey League rules
New since the 2005–06 NHL season, after testing in the American Hockey League, a trapezoid is marked behind each goalie net.
If he plays the puck behind the goal line and not in the trapezoid, a 2-minute minor penalty for delay of game is assessed.
If there is no scoring in the five-minute overtime, the game goes into a three-round shootout with the home team given the choice of shooting or defending first.
If a player crosses the line ahead of the puck but his team is not in possession of it, the linesman will raise his arm to signal a delayed offside; when all players from the offside team leave their offensive zone ("tag up" in the neutral zone) the linesman washes out the delayed call.
When an offside violation occurs, the linesman blows the play dead, and a faceoff is conducted in the neutral zone.
During the 2004–05 lockout, the league removed the "two-line offside pass" rule, which required a stoppage in play if a pass originating from inside a team's defending zone was completed on the offensive side of the center line, unless the puck crossed the line before the player.
The removal of the two-line offside was one of several rule changes intended to increase overall scoring, which had been in decline since the early 1990s.
Icing can also be waved off if, in the officials' opinion, the defending team had a viable opportunity to play the puck before crossing the goal line.
Once a game official drops the puck between the two opposing skaters' sticks, they attempt to gain control of it.
Prior to the 2015–16 NHL season, the away team's centre was required to place his stick on the ice first.
The rule is named for Frank Trushinski, a minor league hockey player for the Kitchener Greenshirts.
In August 1979, John Ziegler Jr., the president of the National Hockey League, announced that protective helmets would become mandatory in the NHL.
However, players who wore helmets without visors prior to the rule change may continue to wear them.
Beginning the 2019–20 NHL season, a player on the ice whose helmet comes off must either pick it up and put it on properly, or skate to the bench (with a reasonable opportunity to complete his immediate play).
Intentionally removing an opponent's helmet during play became a roughing offense punishable with a minor penalty.
In the NHL, the linesmen may also stop play due to player injury, and may report to the referees, during any stoppage in play, any circumstances pertaining to major, match, or misconduct penalties, abuse of officials (physical or otherwise), unsportsmanlike conduct, or double-minor penalties for high-sticking causing injury, that were not detected by the referees.
Small infractions are deemed minor penalties, and the player is kept off the ice for two minutes of gameplay.
A larger infraction such as high-sticking that causes the victimized player to have a visible physical injury is deemed a double-minor, and the perpetrator is kept off the ice for four minutes.
If a goal is scored during the second minor (after the two-minute mark of the power play), the penalty ends.
After a penalty is assessed, play resumes with a face-off in the offending team's defensive zone under most circumstances.
After the 2004–05 NHL lockout, a new rule was instituted that imposes a minor delay-of-game penalty on any defensive player who directs the puck out of bounds (e.g., over the glass into the stands or into the safety netting).
In August 2010, the NHL held an "R & D camp" at the Toronto Maple Leafs’ practice facility, where rule changes under consideration were given trial runs.
Scrimmages at the camp, featuring some top players eligible for the 2011 NHL Entry Draft, experimented with changes such as two-on-two overtime, shallower goal nets, a referee viewing the play from an elevated off-ice platform, and a rink with three face-off circles instead of the traditional five.
